Patent GB-311826-A (GB)
Title: Improvements in electro-magnetic transmitters and receivers for reproducing sound
IPC: H04R9/00
Filed: 1927-11-23
Abstract: 311,826. Sykes, A. F. Nov. 23, 1927. Loud-speakers; diaphragms; magnetic instruments.-Relates to a modification of the invention claimed in Specification 236,313, and consists in electrodynamic sound receiving or transmitting means in which the sound responsive receiving or transmitting member consists of a bag, substantially closed, communicating with or itself forming an air or gas reservoir or sink, the sound waves operating on or being produced by the exterior of the bag. In the construction shown in Figs. I, III, IV and V, a sound responsive silk bag 2 carrying a copper foil strip 1 is hung in the air gap between the poles 3, 4 of an electromagnet comprising limbs 5, 6, yoke 7 and coil 10. Air spaces 8 are provided between the bag and poles 3, 4 and also between the bag and a bronze backing 9 containing the coil 10 and an air pocket or reservoir 11 packed to a greater or less extent with cotton wool 12. A transformer 14 connected to the bag may be mounted on the top of the instrument as shown or in a, cast iron box screwed to one of the magnet limbs. The bag is pushed on to an ebonite spreader 15, Fig. V, and then clamped between a copper plate 16 and a brass clamp 17 bushed with ebonite at 18, the whole being held together in the magnetic air gap by a screw 19. A throttling passage 20 communicates with the reservoir 11, the degree of throttling being controlled either by the tightness of the packing of the wool or by variable mechanical means of the nature of a gas tap. When the passage 20 is entirely closed the bag itself forms the reservoir. The strip 1 is preferably perforated with slits as at 21. The reservoir 11 may communicate with a further channel or series of channels 34. As shown, one such channel crosses the reservoir and may be open at one end to the external air. The bag may be made of re-entrant formation, the elements being arranged in series or parallel, or it may take the form of a rosette. Fig. IX shows various bag sections, that shown at A being perforated at 22 so as to constitute a leaky bag whilst that shown at F has one face non-vibratile by virtue of attachment to a backing 23. The conducting strip 1 may be replaced by a number of turns of wire or or foil. Fig. XI shows a construction employing an annular bag carried by the central pole of a pot magnet which is provided with a channel piece 24 and pole cap 25. The instrument shown in Fig. 1 may be mounted on the top or bottom of a further reservoir, which, as shown in Fig. XIII, may be of honeycomb construction with a parallel or series arrangement of passage ways. A series of valves may be provided as shown at 27, and the reservoir may contain cotton-wool fabrics, flock, feathers, or hair. Alternatively, a series of tubes located in a box or pot filled with grease may be arranged to form a cellular construction or simply a bundle of tubes may be used. Fig. XVI shows a further modification in which the bag 1, 2 is mounted vertically on' an ebonite fitting 15 adapted to be attached to the sound channel, the sound proceeding down the channel to the cast iron base 29 of hollow cellular construction. Gunmetal shroudings 28 surround the windings 10 and the channel 11 is drilled in the shrouding. This channel may be produced through the base 30 and the apparatus placed on a hollow roll of stair carpet &c. so that the hole communicates with the hollow interior of the roll which then forms the reservoir and may contain cotton wool. The different reservoirs may be filled with a gas other than air, such as hydrogen, so as to reduce the inertia effects. The Specification also comprises the combination of any of the instruments hereinbefore described with the instruments or arrangements described in Specifications 160,223, 186,658, 190,759, 190,840, 194,424, 210,956, 220,420, 222,413, 222,924, 227,162, 227,391, 236,313, 252,228 and 263,502.